For simple play applications, bump the application secret on clone.

Fixes an issue where all templates would be cloned with the same
application secret.  For now, we hardcode knowledge of where the conf file is.
A more robust solution involves searching down conf files, but for now this is
probably ok.
Use a slightly more robust mechanism of finding application conf.

Also add a nice reporting message of what the limitations of this approach are.
Merge pull request #9 from typesafehub/wip-jsuereth-application-secret

For simple play applications, bump the application secret on clone.